Method and device for displacing the impact point of a laser beam on a part

Abstract

Method and device for displacing the laser beam on a part by means of a reflexion mirror (20) and focussing lenses (24, 26). A small amplitude motion of the mirror (20) with respect to perpendicular rotational axes crosses at its center is superposed to the motion of the part with respect to the mirror (20) - lenses (24, 26) assembly. The invention applies particularly to the control of the displacement of laser beams used for cutting, marking, and welding parts.

I claim: 
     
       1. A method of displacing the point of impact of a laser beam on a part, the method consisting in directing the laser beam onto a mirror which reflectes it onto the part, and in displacing the mirror support or the part support relative to the other support with a predetermined motion corresponding substantially to the desired trajectory for the beam impact point on the part, characterized in that the method consists in superposing on said motion a small amplitude motion of the mirror (20) relative to its support, in mounting the mirror (20) rotatable about two perpendicular axes (40, 42) which cross at its center, and in determining said small amplitude motion by rotary motion of the mirror (20) about said two axes (40 and 42). 
     
     
       2. A method according to claim 1, characterized in that it consists in suspending the mirror at its center by magnetic attraction and without friction by means of a cushion of air, and in controlling its rotary motion about said axes by varying an electric current flowing through coils (44) fixed to the mirror (20) at points situated on its rotary axes (40, 42) and placed in a fixed magnetic field. 
     
     
       3. A device for displacing the impact point of a laser beam on a part, the device comprising a mirror (20) onto which the laser beam is directed, together with means for displacing the mirror support or the part support relative to the other support with a motion corresponding substantially to the desired trajectory for the laser beam impact point on the part, the device being characterized in that the mirror (20) is mounted to rotate, relative to its support (10), about two perpendicular rotary axes (40, 42) passing through its center, and in that means (44, 80) are provided for displacing the mirror (20) about said two axes with a small amplitude motion which is superposed to the above-specified motion of the mirror support or the part support relative to the other support. 
     
     
       4. A device according to claim 3, characterized in that the mirror (20) is provided at its center with a suspension pivot (34) of the air cushion type, which pivot is subjected to magnetic attraction. 
     
     
       5. A device according to claim 3 or 4, characterized in that the mirror (20) is associated with means (68, 74) preventing its rotation about an axis (30) perpendicular to said rotary axes (40, 42). 
     
     
       6. A device according to claims 3 or 4, characterized in that the mirror (20) includes four arms (38) extending in pairs along the rotary axes (40, 42) and on which coils (44) are fixed symmetrically with their axes perpendicular to the axes of rotation, which coils are movable relative to fixed magnetic circuits (46) carried by the mirror support (10). 
     
     
       7. A device according to claim 6, characterized in that the two coils (44) mounted on a common rotary axis of the mirror are connected in opposition to an electric control circuit. 
     
     
       8. A device according to claims 3 or 4, characterized in that it includes means for measuring the angles of rotation of the mirror about the said axes (40, 42). 
     
     
       9. A device according to claim 8, characterized in that the angle measuring means are linear displacement sensors (66) comprising a moving element guided along an axis which is perpendicular to the two rotary axes of the mirror and carried on a rod (64) which extends axially through one of said coils (44) and is fixed together therewith to the mirror (20). 
     
     
       10. A device according to claim 7, characterized in that the electric control circuit includes an analog function generator (80) associated with a corrector network (84) which is of the proportional-integral-derivative type, for example. 
     
     
       11. A device according to claims 3 or 4, characterized in that it includes dynamic balancing means for the moving assembly constituted by the mirror (20) and its displacement means (44), said balancing means being constituted by a moving assembly (92, 94) which is symmetrical to the said moving assembly (20, 44) and including displacement means identical to those for the mirror (20), but connected in opposition relative thereto. 
     
     
       12. A device according to claim 5 characterized in that the mirror (20) includes four arms (38) extending in pairs along the rotary axes (40, 42) and on which coils (44) are fixed symmetrically with their axes perpendicular to the axes of rotation, which coils are movable relative to fixed magnetic circuits (46) carried by the mirror support (10). 
     
     
       13. A device according to claim 12, characterized in that the two coils (44) mounted on a common rotary axis of the mirror are connected in opposition to an electric control circuit. 
     
     
       14. A device according to claim 13, characterized in that it includes means for measuring the angles of rotation of the mirror about the said axes (40, 42). 
     
     
       15. A device according to claim 14, characterized in that the angle measuring means are linear displacement sensors (66) comprising a moving element guided along an axis which is perpendicular to the two rotary axes of the mirror and carried on a rod (64) which extends axially through one of said coils (44) and is fixed together therewith to the mirror (20). 
     
     
       16. A device according to claim 13, characterized in that the electric control circuit includes an analog function generator (80) associated with a corrector network (84) which is of the proportional-integral-derivative type, for example. 
     
     
       17. A device according to claim 16, characterized in that it includes dynamic balancing means for the moving assembly constituted by the mirror (20) and its displacement means (44), said balancing means being constituted by a moving assembly (92, 94) which is symmetrical to the said moving assembly (20, 44) and including displacement means identical to those for the mirror (20), but connected in opposition relative thereto.